C Program to Read last n characters from the file

C Program to Read last n characters from the file.

⦁ The C library function int fseek(FILE *stream, long int offset, int whence) sets the file position of the stream to the given offset.

⦁ Following is the declaration for fseek( ) function.
int fseek(FILE *stream, long int offset, int whence)

⦁ Stream is the pointer to a FILE object that identifies the stream.

⦁ Offset is the number of bytes to offset from whence.

⦁ Whence is the position from where offset is added. It is specified by one of the following constants.

SEEK_SET - Beginning of file.
SEEK_CUR - Current position of the file pointer
SEEK_END - End of file.

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#include<stdio.h>
int main( )
{
FILE *fp;
char ch;
int num;
long length;
printf("Enter the value of num : ");
scanf("%d", &num);
fp = fopen("test.txt","r");
if(fp == Null)
{
puts("cannot open this file");
exit(1);
}
fseek(fp,0,SEEK_END);
length = ftell(fp);
fseek(fp, (length-num), SEEK_SET);
do
{
ch = fgetc(fp);
putchar(ch);
} while(ch! = EOF);
fclose(fp);
return(0);
}

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Explanation

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⦁ Open file in the Read mode.
fp = fopen("test.txt","r");

⦁ We are moving file pointer to the last location using fseek( ) function and passing SEEK_END constant.
fseek(fp,0,SEEK_END);

⦁ Now evaluate the current position of the file pointer.
length = ftell(fp);

⦁ ftell( ) will tell you the location of file pointer.
File Location = Total Number of Characters on File

⦁ To Read last n characters from the file we need to move pointer to (length-n) character back on the file. and from that location we need to read file.
fseek(fp, (length-num), SEEK_SET);

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Output

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abc

C Program to Read last n characters from the file